Cable Sizing
Insulation type directly determines a cable’s maximum operating temperature — and therefore its base ampacity.
Insulation type isn't just a material choice — it directly determines a cable's maximum safe operating temperature, which is exactly what sets which ampacity table column applies.
| Type | Typical max temperature | Common use |
|---|---|---|
| PVC | 60–75°C depending on formulation | General purpose wiring, widely used across all three codes |
| THHN/THWN-2 | 90°C (dry / wet rated variants) | Common NEC-market conductor, allows higher ampacity for a given size |
| XLPE | 90°C | Common in PEC and AS/NZS markets, particularly for solar DC cable given its UV and thermal resistance |
A higher-temperature-rated insulation allows a higher base ampacity for the identical conductor cross-section — which is exactly why the same physical cable size can show different ampacity figures depending purely on which insulation type is specified.
As covered in the NEC ampacity table article, a high-temperature-rated cable's advantage is capped by whatever the actual termination hardware is rated for — insulation rating and termination rating are two separate limits, and the lower one governs.
Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks